Biological indicators (or “sterility indicators”) are devices that are used to test the efficacy of sterilizers, such as those that are commonly used in hospitals for monitoring processes used to sterilize medical instruments, glassware, etc. The indicators typically include a source of microorganisms, a culture medium, and a detector to indicate the presence or absence of viable microorganisms. The culture medium may also serve as the detector, with formation of a cloudy suspension indicating growth of microorganisms. In practice, the source of microorganisms, typically an absorbent paper strip that has been impregnated with a predetermined quantity of live microorganisms is subjected to a sterilization process. Thereafter, the microorganism impregnated strip is placed in a sterile culture medium and incubated for a predetermined time at an appropriate temperature. At the end of the incubation period, the detector is used to determine whether any microorganisms survived the sterilization process. In some indicators, microorganism survival, which means the sterilization was incomplete, is shown by a change in color of the detector.
To simplify the sterilization test process and minimize the risk that external contamination would affect the test results, the elements of the biological indicator—microorganisms, culture medium, and detector—have sometimes been packaged in a way that permits the microorganism source, culture, and indicator to be combined without exposing the biological indicator to the non-sterile surroundings.
Low-temperature sterilization processes are often used to sterilize objects that may be damaged by the temperature and/or pressure used in steam sterilization processes. Biological indicators have been developed to monitor the efficacy of low-temperature sterilization processes that involve the use of ethylene oxide, hydrogen peroxide, or peracetic acid, for example. Recently, a sterilization system was developed to permit the operator to expose an object to two different low-temperature sterilants. One of the low-temperature sterilants comprises hydrogen peroxide and the other low-temperature sterilant comprises ozone.